构建对象Reducer

//todo Reducer
const todo = (state, action) => {
  switch (action.type) {
    case 'ADD_TODO':
      return {
          id: action.id,
          text: action.text,
          completed: false
        };
    case 'TOGGLE_TODO':
      if (state.id !== action.id) {
        return state;
      }

      return {
        ...state,
        completed: !state.completed
      };
    default:
      return state;
  }
};
//todos Reducer  [数组状态]
const todos = (state = [], action) => {
  switch (action.type) {
    case 'ADD_TODO':
      return [
        ...state,
        todo(undefined, action)
      ];
    case 'TOGGLE_TODO':
      return state.map(t => todo(t, action));
    default:
      return state;
  }
};

//visibilityFilter Reducer
const visibilityFilter = (state = 'SHOW_ALL',
  action) => {
  switch (action.type) {
    case 'SET_VISIBILITY_FILTER':
      return action.filter;
    default:
      return state;      
  }
};

//todoApp Reducer [对象状态]
const todoApp = (state = {}, action) => {
  return {
    todos: todos(
      state.todos,
      action
    ),
    visibilityFilter: visibilityFilter(
      state.visibilityFilter,
      action
    )
  };
};

const { createStore } = Redux;
const store = createStore(todoApp);

console.log('初始化状态:');
console.log(store.getState());
console.log('--------------');


console.log('触发 ADD_TODO:');
store.dispatch({
  type: 'ADD_TODO',
  id: 0,
  text: 'Learn Redux'
});
console.log('当前状态:');
console.log(store.getState());
console.log('--------------');

console.log('触发 ADD_TODO:');
store.dispatch({
  type: 'ADD_TODO',
  id: 1,
  text: 'Go Shopping'
});
console.log('当前状态:');
console.log(store.getState());
console.log('--------------');


console.log('触发 TOGGLE_TODO');
store.dispatch({
  type: 'TOGGLE_TODO',
  id: 0
});
console.log('当前状态:');
console.log(store.getState());
console.log('--------------');



console.log('触发 SET_VISIBILITY_FILTER');
store.dispatch({
  type: 'SET_VISIBILITY_FILTER',
  filter: 'SHOW_COMPLETED'
});
console.log('当前状态:');
console.log(store.getState());
console.log('--------------');

//最终代码： http://jsbin.com/qopatey/edit?js,console